It is often beneficial to provide downhole heat in oil and/or gas wells and similar environments. For example, heat can be delivered to the production tubing in the well via a heater installation in order to heat the oil to be extracted, reducing its viscosity and improving extraction rates. In another example for heavy oil production, the heater installation can deliver heat to the oil reservoir itself to increase the amount of oil that enters the production tubing. Existing downhole heater installations typically require the use of a drilling or other rig. Further, the installation of a heater is usually managed by clamping heater cables to the exterior of the production tubing, which generally requires that a complete workover or similar operation must be performed. Such operations can be very time consuming and expensive processes.
In certain circumstances, heating systems of the present invention can be deployed within continuous tubing, frequently referred to as “coiled tubing” because it is sufficiently flexible to be coiled onto a spool and transported to the deployment site. Deployment of coiled tubing heaters improves heat transfer to a target medium because such coiled tubing heaters provide a larger surface area in contact with said medium, and can frequently be installed so as to be in direct contact with said medium. Further, because exposure of heater cables to well fluids can be problematic due to the chemical makeup of such fluids, installation of such heater cables within coiled tubing isolates and protects heater cables from such well fluids. In many applications, such continuous tubing heating devices can be installed without performing a workover, or requiring the use of a drilling or other rig.
Electric cables typically do not have sufficient tensile strength to be deployed independently within a tube, especially over relatively long vertical sections. Accordingly, various means of providing support to heater cables have been designed including, without limitation, for downhole skin-effect heaters like the skin-effect heating cable described in co-pending United States Patent Application Publication No. 2011/0233192, entitled “SKIN EFFECT HEATING SYSTEM HAVING IMPROVED HEAT TRANSFER AND WIRE SUPPORT CHARACTERISTICS”, which is incorporated herein by reference. Unfortunately, such existing methods are generally not suitable to use with multiple independent cables, such as mineral insulated (“MI”) cables, that comprise their own electrical circuit and do not need to be electrically attached to the coiled tubing to function.
In some cases, simple banding or clamping materials have been used to support cables in a desired position, including binding such cables to support rope. However, simple banding can come loose, particularly after thermal cycling of heating elements. Other methods of installing cables into tubes have been utilized in the oil and gas industry include: crimping the tube to the cables; using helical buckling to self support the cables; using high strength conductor materials; and tightly forming the tube over the cable during the tube manufacturing process. However, none of these methods provide the benefits of the present invention, which further addresses problems associated with supporting of heating cables and tubing containing such heating cables.